Field of the Invention
This invention relates to a semiconductor wafer clamp for clamping two wafers together in alignment, and more particularly, to a wafer clamp that clamps two wafers together in alignment using a pressure differential between a vacuum created between the wafer-clamping surfaces of the clamp and the ambient environment surrounding the wafer clamp.
Description of Related Art
Wafer-to-wafer bonding is used in a wide range of semiconductor fabrication applications for forming semiconductor devices. Wafer-to-wafer bonding involves the aligning of two wafer surfaces in contact with one another and then forming a bond interface between the two. The quality of the wafer-to-wafer bond largely depends upon the preservation of the alignment of the two wafers.
Prior to bonding, the opposing surfaces of two wafers are aligned, placed in contact with one another, and then held together by a wafer clamp. The purpose of the wafer clamp is to prevent relative motion between wafers during transport from an alignment tool to a permanent bonding tool. A typical wafer clamp includes first and second wafer holding elements and a clamping mechanism. The wafers are typically placed in contact with and held in contact with the respective wafer-clamping elements by electrostatic attraction. The clamp is then used to maintain the relative position between the two wafer holding elements. This is achieved typically by using the clamp to apply a clamping force to the two wafer holding elements or by stiffly connecting the wafer holding elements to one another.
The above-described wafer clamp is problematic. The clamping force applied to the first and second wafer holding elements tend to create lateral forces on the first and second wafers, which in turn, may cause the wafers to become misaligned. With misalignment, the bonding of the two wafers may be less than ideal.